Hydrothermal synthesis of quartz



Aug. 28, 1962 Filed Sept. 6, 1956 J.hA.JCDET HYDROTHERMAL SYNTHESIS OFQUARTZ 2 Sheets-Sheet 1 INVEN TOR.

JACOB M.JOST

ATTORNEY Aug. 28, 1962 J. M. JosT 3,051,558

HYDROTHERMAL SYNTHESIS OF QUARTZ Filed Sept. 6, 1956 2 Sheets-Sheet 2INVENToR. JACOB M .JOST

ATTORNEY 3,951,558 HYDRGTHERMAL SYNTHESIS F QUARTZ Jacob M. Jost,Cleveland, (fihio, assigner to Clevite Corporation, Cleveland, hio, acorporation of Ohio Filed Sept. 6, 1956, Ser. No. 698,334 l2 Claims.(Cl. 23a-273) This invention relates to methods and apparatus for thehydrothermal synthesis of quartz in the form of single crystals.

'Ihe term hydrothermal synthesis is used herein to designate acrystallization process, carried on at relatively high temperatures andpressures, wherein the material to be crystallized is dissolvedessentially to saturation in a uid transfer medium at one temperatureand deposited on a seed body at `a lower temperature. In its generalaspects, the process and many variations are well known and have beenyapplied to the production of crystals of vanious materials in additionto quartz.

As applied to quartz synthesis, the hydrothermal process requires theuse of high pressures and temperatures in order to effect sufficientdissolution of the supply material (e.g., crystalline silica) to renderthe process feasible from a practical standpoint. Apparatus for carryingout such a process are known and may be referred to as autoclaves Whilethe first successful synthesis of crystalline quartz dates back severaldecades it was not until recently that crystals of potentially usefulsize could be produced and even more recently that the production ofsynthetic quartz crystals in commercial quantities, qualities and sizeshas been realized. Such production can be and has been accomplished bythe use of the method and apparatus disclosed in U.S. Letters Patent No.2,575,303 to Sobek and Hale and assigned to the same assignee as thepresent invention. Reference to this patent may be had for a completeexplanation and the details of the hydrothermal process as applied toquartz synthesis.

At the present time quartz crystals, natural or synthetic, findextensive applications in the optical and electronic industries. Whilethe most important use for such crystals is for the fabrication ofoscillator plates used for frequency control, all known electronic andoptical uses for quartz crystal require the crystals to be free fromsubstantial impurities, physical defects, electrical and opticaltwinning, etc. Crystals of suitable quality are referred to as being ofelectronic grade or optical grade as the cas-e may be.

Aside from the fact synthetic quartz obviates the necessity ofdependence on foreign sources, it has many other inherent 'advantagesover natural quartz, particularly: (l) the quality is better and issubject to control and (2) the size and shape of the grown crystals are,to a great degree, subject to selective variation to obtain dimensionsand congurations best suited to the eicient fabrication of the crystalelement to be manufactured. Thus, for example, by use of a seed body ofparticular dimensions and/ or orientation relative to itscrystallographic axes a crystal can be grown which is of optimum sizeand shape to enable cutting of oscillator plates with a minimum of time,labor and waste. The sole advantage of natural quartz existingheretofore has been its lower cost in terms of price per pound of rawmaterial; this is largely olfset by labor and waste reductions Iaccruingto the use of synthetic quartz in fabricating quartz elements. t

It is the fundamental object of the present invention to provide animproved apparatus for hydrothermal synthesis of quartz which overcomesone or more of the disadvantages of prior art apparatus.

Thus, it is ya more specific object to provide apparatus which is morecompact, simpler in construction, [and less expensive in iirst,maintenance, and operating cost than any known heretofore.

E Patented Aug. 23, 1962 Another object of the invention is theprovision of apartus for producing quartz in high quality single crystalform at -low cost and at ya high production rate per unit of apparatus.

Still another object is the provision of apparatus which enables theproduction of relatively large quantities of high quality quartzcrystals per single `apparatus unit with a minimum variation in size-and/ or quality of crystals in a batch.

A further object is the provision of apparatus for quartz synthesiswhich provides improved circulation of the transfer medium `and embodiesyno moving parts.

rl'hese and other advantages of the invention will be yapparent to thoseskilled in the art from a reading of the following description andsubjoined claims in conjunction with the annexed drawings.

The present invention contemplates apparatus for the hydrothermalsynthesis of quartz in single crystal form which comprises a verticallyelongated enclosed chamber adapted to contain a uid transfer mediumunder conditions of high temperature and pressure. The chamber has aquartz growing region and, therebelow, a sourcematerial supply region.Means are provided to supply heat to the lower end of the chamber and tocontrol circulation of the iiuid transfer medium in the chamber,directing the convectional flow upwardly lalong the walls of the chamberin the growing region and centrally axially downward through the growingregion Iinto the supply region.

According to a particular feature of the invention, the circulationcontrol means, which includes a baille interposed between the growingand supply regions, is so constructed and arranged as to define `andlimit flow communicatio-n between the two regions to an upward and adownward flow-passage, jointly controlling and directing theconvectional flow of the transfer medium. Each of the dow-passages isrestricted, individually and collectively having cross-sectional areasrelatively small in comparison to that of the chamber. The downwardflowpassage is substantially centrally located with respect to thevertical center-line of the chamber while the upward flow-passage islocated adjacent the lateral margin of the chamber and opens tinto thegrowing region yat a substantial distance above the level where thedownward flow-passage opens into the supply region.

In the drawings:

FIGURE 1 is a vertical sectional view of quartz synthesizing apparatus,viz., an autoclave, according to the present invention;

FIGS. 2 and 3 are Ihorizontal cross-sectional views taken, respectively,on lines 2 2 and 3 3 of FIG- URE l;

FIGURE 4 is a schematic view of a portion of the structure shown inFIGURE l;

FIGURE 5 is a schematic view similar to FIGURE 4 showing a modified formof the invention;

FIGURES 6., 7 and 8 are fragmentary vertical sectional views of variousadditional modifications of the invention taken, respectively, on lines6 6, 7 7 and 8 8 of FIGURES 9, l0 and 11, and

FIGURES 9, l0 and ll are top plan views corresponding respectively to|FIGURES 6, 7 and 8.

In FIGURE 1 there is illustrated in substantial detail a verticalautoclave 20 embodying the present invention in one of its preferredforms. Thus Vautoclave 20 comprises means ideiining `a verticallyelongated enclosed chamber 22.. The chamber defining means include acylindrical heavy-walled pressure vessel 24, having an integral bottomwall 26, and a threadedly removable upper end closure assembly 28.Pressure vessel 24 is mounted in a vertical position on a flat plate 30supsteels or equivalent.

ported by a parir of channel irons 32 which in turn are ,24 should befabricated of a suitable metal or alloy which Will provide sufhcientmechanical strength to withstand such conditions for relatively longperiods of time without danger of rupture or leakage. In addition theinternal surfaces of pressure vessel 24 and all surfaces exposed to theinterior chamber 22 should not be subject to appreciable corrosion by,or otherwise susceptible to reaction with, the fluid transfer mediumcontained in the vchamber as hereinafter explained. To `fulfill thesere- Y quiremen-ts it is preferred that the pressure vessel 24 befabricated of alloy steel such as 400 series type stainless Where lowertemperatures and pressures are used, carbon steels are satisfactory.

As best shown in FIGURE 4, chamber 22 has a growing region 36 in itsupper end anda source material supply region 38 in its lower end. Byupper'and lower end it is meant to signify that the growing region 36 isabove or uppermost in chamber 22 with respect to supply region 38 andnot that each region occupies any particular proportion of the totallength of the chamber. From the standpoint of production economy it isdesirable that the growing region occupy as great a percentage of theVvolume of chamber 22 as consistent with the operating conditions andprinciples hereinafter set forth. In most cases lthe growing regionwould occupy, at least, ap-

, proximately the upper half of the length of chamber 22.

For reasons which will become apparent as the Vdescription proceeds, itis preferred that chamber 22 is generally cylindrical and has an axialor vertical dimension large in comparison to its diameter. In itspreferred form chamber 22 would have a length-to-diameter .ratio (aspectratio) in the range from about 5:1 to 15:1 and the quartz growing region36 would occupy somewhat more than the upper half of the length of thechamber, the remainder being Vdevoted principally to the supply ,region38.

Means are provided for supplying heat tothe lower end of chamber 22 suchmeans taking the form of a plurality 'of electrical heater elements 40,secured to the underside of plate 30 adjacent the bottom of pressurevessel 24, and perimeter heater elements 42 enveloping the lower Y endof the VesselV along substantially the entire length of the supplyregion 3S. Heater elementsv40 and 42 are connected to `a source (notshown) of electrical power through suitable controls, manual orautomatic, which Y enable regulation of the amount of heat suppliedthereby.

'Ihe electrical connections and controls for heater ele- Vments 40 and42, being ofV conventional design, are'not shown in the drawing.

'The lower portion of vessel 24, which'deti'nes Aand enclosessupply'region 38 of chamber'22, including the .heater elements, isencased in' ia suitable heat insulating .material 44 so as tosubstantially'preclude or at least fminmize heat loss from the supplyregion.V yThe remainder of the pressure vessel is covered with laggingor thermal insulation 46 of lesser effectiveness so as to allow aselected pattern and amount of heat rejection from growing region 36through the walls of pressure vessel 24. The type and quantity ofinsulation material .applied around the growing region 36, inconjunction with other factors presently to be explained, establishes aselected negative temperature differential between the supply region 381and growing region 36 of chamber 22.

Within the growing region 36 of chamber 22 are pro-V vvided crystalholders or racks 48 which serve to mount a .plurality of Yseed bodies inspaced relationship so that 4 each seed body is exposed to the fluidtransfer medium. In FIGURE l, the racks are illustrated as being filledwith grown crystals 50 rather than seed bodies. The crystal racks areremovably supported within the vessel 24 by any suitable mechanicalarrangementgfor example, the racks may ber suspended from the closureassembly 28 or supported on other structure occupying the lower portionof chamber 22 as hereinafter described. However, regardless of the formof 'the racks or the manner in which they are supported within thevessel they must be so constructed and arranged as to securely hold theseed bodies and the resulting grown crystals in spaced relation to thesurrounding inner wall of vessel 24; that is, `so that an unobstructedannular clearance space 52, extending the entire length of growingregion 36, exists between the loaded crystal racks and the inner Wall ofvessel 24. The width or radial dimension of clearance space 52 is animportant detail; suitable values of this Adimension will be apparenttfrom the description hereinbelow of other structure and conditionswhich inuence Ithese values.

Preferably, the inner surface 5 4 of the bottom wall 26 of vessel 24 ishemispherical, as shown in FIGURE l; however, any concave curvaturewould be satisfactory and even a ilat surface would be operative to adegree.

vAt a short distance above the inner bottom surface `54 ,is an annularshoulder 56 which supports a container 58 for supply material (eg.crystalline silica) disposed in supply region 38.

Container 58 is fabricated almost entirely of a perforate material suchas Wire mesh., expanded metal, or sheet metal containing a large numberof holes. In the illustrated embodiment, container 58 takes the form ofan elongated hollow cylinder of wire mesh, as best appears in FIGURE 4.Thus, the container comprises a .concentric cylindrical outer wall 60and inner wall 62,

lboth of wire mesh. The bottom 64 of the hollow cylinder is also formedof wire mesh, as are a number of transverse annular partions 66 whichdivide the cylinder into a number of separate compartments 68. The topof container 58 is formed by a solid plate l69 which, except for acentral opening '70 in the plate, fills the cross-sec- Ytion of chamber22. Outer container Wall y60 is of lesser diameter than chamber 22 withthe result that an annular clearance space 72 is formed between the twowhich extends the entire length of the container.

While a container 58 of cylindrical shape has been shown and described,it willV be understood that other cross-sectional configurations maybeemployed. Thus, for example, the outer wall might have `a triangularcrosssection with its apices in contact with the walls of chamber 22 sothat, instead of a single annular clearance space 72, there would bethree functionally equivalent clear- Iance spaces dened between thechamber wall and the respective sides of the container. Y Alternatively,the triangular cross-section might be smaller so that the apices do notcontact the chamber wall. In like manner, the

- cross-section of the container may be a square, hexagon or otherpolygon provided that, in any case a clearance space functionallyequivalent to 72 is defined.

Coaxially extending through the central opening of Vcontainer 58 is atubular member 74, the lower end of which terminates Hush with thebottom 64 thereof. The

upper end of tubular member 74 extends through opening and projects ashort distance above top plate 69 of container 58. VThe outer diameterof tubular member 74 is smaller than the opening 70 and the innerdiameter of inner wall 62 of container 58 so that annular clearancespaces 76 and 77 remain around the tubular member. Connected to orformed integrally with the upper end of tubular member 74 is a baiemember 78 in theform VVof a funnel or hollow cone concentricallydisposed in v" chamber 22 between growing region 36 and supply region 38with its large circumference uppermost. Baffie member 78 and tubularmember 74 jointly comprise a 39 ilow control means for the fluidtransfer medium. To this end, the lower end of baille 78 contains acentral opening 80 in ilow communication with the interior 8l of tubularmember 74 which is, effectively, an extension of the baille member and,with opening 80, constitutes a downward llow passage for the fluidtransfer medium.

The circumference of the upper end of baffle 78 is appreciably smallerthan that of chamber 22 so that an annular clearance 32 remains betweenthe perimeter of the baille and the surrounding wall of the chamberinterrupted only by a diametral bracket member 84 secured to or integralwith the baille. Bracket 34 serves to center the baille and may providea support for seed racks 48.

The present invention contemplates and includes certain importantdetails as to relative dimensions and essential features f variouselements; however, inasmuch as these details are closely related tooperating conditions in chamber 22, their disclosure will be simplified`and more lucid in the light of the following explanation of the generaloperation and `function of the apparatus as thus far described.

The individual compartments 68 of container 53 are filled with asuitable source of quartz, for example, crystalline silica 85, in largeenough particle sizes as to prevent close packing. The amount of silicaused should materially exceed that to be consumed in the run so thatessentially complete saturation of the transfer medium at the dissolvingtemperature is maintained at all times.

Seed racks 48 are loaded with seed bodies of the desiredcrystallographic orientation, size and shape and installed, the chamber22 is filled with a fluid transfer medium to about 70 or 80% of itscapacity (the degree of filling and operating temperature determines theoperating pressure), and the closure assembly 2S is secured in place.Satisfactory transfer mediums include, for example, an 0.83 molaraqueous solution of sodium carbonate (Na2CO3) or an aqueous solution ofsodium carbonate and sodium acid carbonate (NaHCO3) in amounts of 1 moland 1/16 mol per liter, respectively. The preferred range of operatingtemperatures is from 280 to 370 C. with a differential of 5 to 25 C.between the average temperatures of the supply and growing regions (thelatter being cooler). The operating pressure range is from 1200 to10,000 pounds per square inch `and the degree of initial filling isselected on the basis of the intended operating temperature and vaporpressure or thermal expansion characteristics of the fluid transfermedium `to achieve the desired pressure. The operating pressure is afunction of temperature and vapor pressure if the chamber 22 contains avapor space at operating conditions; otherwise the pressure is afunction of temperature and the coefficient of thermal expansion of thefluid.

The autoclave having been loaded, the run is started by turning on thepower to heater elements 40 and 42. Due to the location of the heatinput, the relative disposition of the supply and growing regions, andthe location and configuration of flow control means 74, 78,convectional circulation of the fluid medium results in a flow patternwhich will now be described with reference to FIGURE 4, wherein theheavy-line arrows indicate the direction of iluid flow.

The fluid in the lower end (supply region 38) of chamber 22 is heatedand concomitantly decreases in density. This causes the lluid to rise inclearance spaces 72 and 76. The upward movement of fluid in clearancespace 72 of the supply region 3S is limited by plate 69; therefore, thisfluid passes laterally inwardly and upwardly through the perforate wallsof container 50 and the interstices between particles of the crystallinesilica supply material S5 into cleara ce space '76. When the fluidtemperature has reached a sulllciently high value the fluid, in itspassage through the container 58 and its contents, it dissolves andcarries with it an amount of silica until saturated. As thesilica-bearing or nutrient iluid arrives in space 76, displacing thetransfer medium originally occupying space 76, it passes upwardly aroundtubular member 74 through space 77 whereafter it encounters theunderside of baille 78 which directs the llow radially outward towardannular upward tlow-passage 82 between the periphery of the large end ofthe baille member 78 and the wall of chamber 22. The upward flow-passage82 channels the upwardly moving lluid into a relatively thin boundarylayer along the wall of 4the growing region 36. This boundary layer llowoccupies clearance space S2 and a major portion of the flow continuesupwardly to the top of the chamber 22. Some part of the upward flowbranches olf inwardly before reaching the top of chamber 22, passingover and among the seeds and racks, 48, 50. The width of space 52 shouldbe sufficient to accommodate this upward flow but not wider thannecessary because this would curtail the space available for racks andcrystals 48, 50.

irnultaneously with the upward tlow of uid just described, the coolerand, therefore, denser fluid in the central part of growing region 36ows axially downwardly over and among the seed bodies in racks 48. Thisdownward flow continues to baille 78, the upper side of which deflectsthe ilow radially inwardly toward the downward flow-passage comprisingcentral opening 80 and the interior 81 of tubular member 74.

The rate of circulation and the negativeY temperature gradient existingwhen equilibrium conditions obtained are interrelated and `are primarilya function of or iniluenced by several factors which will now beenumerated and discussed.

(l) The aspect ratio (i.e., the length-to-diameter ratio) of chamber 22:lt will be appreciated that attainment of satisfactory convectionalcirculation depends on an adequate vertical temperature gradient. Itfollows, therefore, that a short, squat or horizontally elongatedchamber would not be conducive to proper circulation; the chamber musthave a length great in comparison with its diameter. ln practice it hasbeen found that an aspect ratio of at least 5:1 and preferably 10:1 or15:1 gives the best results.

(2) Percentage opening provided by baille member 78: This factor refersto the aggregate minimum cross-sectional area of the flow-passagesthrough which the growing and supply regions are in ilow communication,expressed in terms of a percentage of the total cross-sectional area ofchamber 22. Thus, in FIGURES 1 and 4, the flow-passage area for upwardllow is either the `area of the annular space 82 or the annular space 77ybetween the exterior of tubular member 74 and lthe periphery of opening70 in plate 69, whichever is lesser. At this juncture it is pointed outthat either of these annular dow-passages, S2 Ior 77, may be dimensionedto control the rate of upward flow; by using the latter (77), thethickness of the boundary layer of upward llow (which is influenced bypassage 82) may be varied independently .of the flow rate.

The minimum flow-passage area for downward ow is either the area of thecentral opening 80 in baille 78 or the cross-sectional area 'of theinterior 81 of tubular member 74, whichever is lesser. In practice ithas been found that best results are obtained where the percentageopening is in the approximate range 3 to 20%, and where the minimumareas of the upward and downward flowpassages are roughly equal.

The percentage opening, controlling the ilow rate, exerts a stronginfluence on the temperature gradient which in turn also 'affects theilow rate.

(3) Vertical distance between uppermost terminus of upward and lcwermostterminus of downward flow-passages: lt will be appreciated that in orderto obtain the circulation pattern described above, a densitydifferential must exist between the iluid in the vicinity of therespective flow-passages. Since the density gradient exists by virtue ofthe temperature gradient, the upper terminus of the upward How-passagemust be located a substantial distance above the pointwhere the downwardnow-passage opens into the supply region. The distance -must be'sufficient to obtain a substantial density differential pressure headbetween the two locations. In FIG- URES 1 and 4, the effective distanceis that measured from yspace 82 to the bottom end of tubular member 74.

If the upper terminus of the upward owapassage and Vthe lower terminusof the downward How-passage were in the same horizontal plane,as, forexample, if baille member 78 were an annular plate, without tubularmember 74, the upward ow would be through the central as well vas theperipheral passage and, while the upward flow adjacent the walls mightlbe more vigorous because the fluid there would vbe hotter, littlecirculation, if any, of the pattern described would result and therewould be considerable turbulence due to the conflict of upward anddownward flow in the axial region of chamber 22. It should beunderstood, however, that while the conical shape of bale member 78 isof considerable advantage in reducing turbulence and achieving lateralseparation of the counterow, workable circulation can be obtainedWithout this shape, Thus, referring again to the abovementionedunsatisfactory annular plate baffle, such a baille is operative whenused in conjunction with a tubu- 'lar member such as 74, as illustratedin FIGURES 8 and 1l and hereinafter described in more detail. This ismentioned at this juncture to emphasize the fact that satisfactorycirculation stems primarily from the location of the upper terminus ofupward flow-passage 82 a good distance above the lower terminus of thedownward iiowpassage. If -thisrelation does not exist, the circulationis inadequate and/ or otherwise unsatisfactory; if the relation isreversed, i.e., if the lower terminus of the central how-passage isuppermost (for example, where the baille V78 is inverted from theillustrated position) the direction of circulation would be reversed andthis would not be operative to accomplish the objects of the inventionas ywill be explained hereinbelow.

The vertical distance between the upward and downward How-passages, likeall other factors under discussion, is so interrelated with otherfactors and conditions as to preclude specification `of an inflexiblenumerical value, However, depending on the aspect ratio of chamber 22,the percentage opening of the baiile, the temperature gradient, etc.,the distance would amount to at least about land preferably 30 or 40%kof the length of chamber 22. In general, smaller percentages are moresuited to autoclaves wherein the volume of chamber 22Vis relativelysmall.

(4) Heat supply and insulation: The (negative) temperature differentialbetween the growing and supply regions, as well as the verticaltemperature gradients are closely related to the location, arrangementand relative effectiveness of the heater elements 40 and 42 andinsulation 44 and 46. Apparatus of the type described and illustrated inFIGURE l may be operated success fully with either bottom heaters (40)Ior peripheral heaters (42) only but the combination of both ispreferred. In any case the heating capicity of the heaters used must besucient -to raise the average temperature of the transfer fluid to theoperating range (280 to 370 C.) in a reasonable time and maintain thedesired .temperature and Atemperature gradient (5- to 25 C.) in view ofthe heat loss permitted by the insulation 44 and 46 and the circulationrate. A full complement yof heaters may be used to kbring :the apparatusto equilibrium Voperating temperature and then part of fthe heaters cutout or the power supply -to the entire complement reduced.

Preferably the heater complement and insulation 44 cover the bottom ofvessel 24 and envelop the sides up to the upper limit of the supplyregion, which coincides approximately with the top end of container 58.The insulation of supply region 38 preferably is of maximumeffectiveness in order -to minimize the operating power requirements.The insulation 46 surrounding growing S region 36u is `ofsucienteectiveness to allow a selected rate and pattern of heat lossthrough the surrounding walls of vessel 24.

It will be understood that suitable conventional thermocouples andpressure gages (not shown in the drawings) may be utilized to determine,establish and maintain desired operating conditions. Y

The temperature distribution and heat transfer within the chamber atequilibrium is generally as follows: The transfer mediumris at itshighest temperature in supply region 38, specifically in the lowerreachesrof clearance space 72; this is lbecause the transfer medium isheated during its downward ilow through tubular member 74 .by heattransfer from the hotter ascending fluid surrounding member 74 and Visfurther heated by its proximity to the heated -bottom 26 and lowersidewalls at vessel 24 during the time the fluid issues from the lowerend of member 74 and reverses its direction. The lowest temperature ofthe transfer medium usually occurs near the top of the growing regionowing to the fact that it has previously ascended the length of thegrowing region in a relatively thin layer along the walls of vessel 24,continuously giving up heat to the walls. The temperature of thedescending fluid in the growing region at the upper side of baiiie '78is usually slightly higher than at the top of the growing region byreason of having mixed with ow branching inwardly from the main upwardcurrent in clearance space 52. The temperature differential (negative)between the ybottom 4and top of the growing region account for al1 orthe major part of the 5 to 25 C. differential between the averagetemperatures of the supply and growing regions. In consequence of thelow pattern and temperature distribution achieved, the descending llowof fluid in growing region 36 remains at substantially a constanttemperature because it is surroundedyby the upward ilow in space 52which, at any given horizontal level, is `at about the same or a highertemperature than'the downward tlow at that level, thus preventing heatloss from the downward flow. In other words, the temperaturedifferential necessary for crystal growth is established during theascent of the transfer fluid in space 52 while it is out of contact withthe seed bodies. Thereafter, the growing is accomplishedV by thedescending uid under practically isothermal conditions in the growingregion. The result, aside from a high thermal eiliciency and consequentlow power cost per pound of crystal, is a `substantially uniform growthrate on all seed bodies regardless of location in the growing region.The variation in the weight of crystals grown in apparatus according tothe invention is only i5% as compared to m20 to 40% in conventionalapparatus.

Compartmentation of the supply container 5,8 is not essential Vbutimproves circulation and serves to maintain a fairly `constant relationand maximum contact between the supply material and the circulatingfluid; otherwise, as the run progresses the unconsumed supply materialsettles to the bottom of the container where it is bypassed lby some ofthe uid moving upwardly in the supply region. t

A detailed description has fbeen given of one preferred form ofapparatus -according to the present invention. Many variations arepossible in the physical structure of the apparatus illustrated inFIGURE 1 which also give satisfactory results by virtue of the fact thatgenerally the same growing conditions may be achieved with a modifiedconfiguration. j Inasrnuch as these modifications relate to thecirculation control means and/ or the disposition of the supplymaterial, the following description of examples of such modifications isrestricted to these features.

FIGURE 5 is a schematic view similar to FIGURE 4 showing a somewhatsimpliiied apparatus which may be preferred for smaller units. In FIGURE5 parts in common with FIGURES l to 4 are identified with the samereference numerals with a lower case letter appended in instances wherethe designated part is modified. This same system of designation isadhered to throughout the description of various modillcationshereinbelow.

lt will be readily apparent from an inspection of FIG- URE that itschief distinctions over the previously described apparatus resides inits simplification by the elimination of the tubular member 71.- `aridsupply container 53. Thus the ilow control means comprises baille member'7S which takes the form of a simple hollow, truncated cone coaxiallydisposed in chamber 22 between the growing region 36 and supply region33 with its apex pointing downwardly. inasmuch as FGURE 5 is a schematicdrawing, the manner in which baille member 78 is Supported is not shown.lt will be understood, hcweve that mounting of baille member 7S may beaccomplished as shown in FlGURE l or by any other suitable means. Tosimplify loading of the supply material the baille mounting shouldpermit its easy removal. Furthermore, such mounting need not possesssubstantial mechanical strength unless used to support the crystals andracks 43, 5@ and then only sufficient to accomplish this purpose.

ln the FGURE 5 apparatus, the supply material 85, is placed loose in thebottom of chamber 22. ln the absence of a container therefor, it may bedesirable that the material be in the form of relatively larger chunksto provide interstices of large volume to facilitate circulationtherethrough of the transfer medium. The general overall functioning ofthe apparatus is essentially the same as that already described.

FGURES l and 4 on One hand and FGURE 5 on the other are illustrative or"two basic variations of the apparatus, namely, the presence or absenceof the supply container 58 and of the tubular member 7d. Either of thesebasic variations may be further modiiled in the specilic conguration ofbaille member 73.

Thus, FiGUliS 6 and 9 illustrate a baille member 75u of generallyconical configuration but having curved instead of straight sides sothat the baille resembles a hollow spherical or parabolic section havingits underside convex and its upperside concave. Batlle 73a is shown ashaving a coaxial hollow tubular appendage 74a extending downwardlytoward the supply chamber. This appendage may extend, or be connected toa tubular member (such as 74, FGURES l and 2) which extends, to within ashort distance of the bottom of chamber 22. Alternatively the appendage74a may be quite short and serve merely to concentrate and givedirection to the downward iiuid ilow therein.

Bafrle member 78a is supported by three or more (-four shown) peripheralears 84a, analogous to bracket S4, `FGURE. l, which frictionally engagethe inner surface of vessel 24.

FIGURES 7 and l0 illustrate another orm of baille, 78]), which issimilar in configuration to baille 73 but has a hollow cylindricalcoaxial skirt 5 extending upwardly from its large diameter end. Theradially outer Surface of skirt S5 is inwardly from the walls of vessel24 by an amount substantially equal to the radial dimension of clearancespace 52. ln addition to giving direction to the upward ilow or" thetransfer medium and assisting the establishment of a hollow cylindricalflow path in growing region 36, skirt 86 prevents the rising lluid frombeing drawn radially inwardly after clearing the baille by thedownwardly ilowing fluid entering the baille from above.

Batlle member 7551: is centered and lsupported in chamber 22 by a numberof radial spring loops 84b which frictionally engage the inner wall ofvessel 24.

As previously mentioned, the baille member may take the form of a flatannular plate having a tubular member such as 74 extending downwardlyfrom the central aperture therein. Baflle member 78C, FIGURES 8 and ll,is a baille of this type. vIt is re-stated that in such a baille,tubular member 74 is not optional; it is essential and must be ofsullicient length to effect substantial longitudinal spacing of theupper terminus of the upward dow-passage above the lower terminus ofdownward flowpassage.

As shown in FIGURES 8 and ll, baille member 78C is a ilat, annular platecentered and supported in chamber 22 by a number of `symmetricallyspaced spring loops 84h. Tubular member 74 has its upper end fitted intothe central aperture of the plate. The lower end of the tubular memberends downwardly in the ysupply region by an amount suiiicient to utilizethe density differential to cause circulation as already explained. Itis pointed out that the necessity of having the tubular ymember 74 doesnot carry with it the need of a container for the supply materialalthough the container simplities the matter of getting the tubularymember through the material.

While there have been described what are at present considered to be thepreferred embodiments of the invei n, it wili be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is, therefore,aimed in the appended claims to cover all such changes and modificationsas fall within the true spirit and scope of the invention.

l claim:

l. Apparatus for the hydrothermal synthesis of quartz in single crystalform comprising: means dening a vertically elongated enclosed chamberadapted to contain a fluid transfer medium under conditions of hightemperature and pressure, said chamber having a quartz growing region inits upper end and a source material supply region in its lower end;means operative to supply heat to the lower end of said chamber; andcirculation control means in said chamber including a baille interposedbetween said growing and supply regions, said circulation control meansbeing so constructed and arranged as to define, and limit flowcommunication between said regions to, an upward ilow passage and adownward flow passage, jointly controlling and directing theconvectional ilow of such a iluid transfer medium due to heat suppliedby said heat supply means, each of said passages, individually having across-sectional area relatively small in comparison to that of saidchamber, said downward flow-passage being substantially centrallylocated with respect to the vertical centerline of said chamber, saidupward flow-passage being located adjacent the laterally outer limits ofsaid chamber and opening into said growing region a substantial distanceabove the location where said downward ilow passage opens into saidsupply region.

2. Apparatus for the hydrothermal synthesis of quartz, in single crystalform, comprising: means dening a Vertically elongated enclosedcylindrical chamber the length of `which exceeds the diameter by afactor of at least about 5, said chamber being adapted to contain afluid transfer medium under conditions of high temperature and pressureand having a quartz growing region occupying, at least, approximatelythe upper half of said chamber, and a source material supply region inits lower end; means operative to supply heat to the lower end of saidchamber; said heat supply means being of suilicient capacity toestablish and maintain an average temperature of at least 280 C. in suchiluid; and circulation control means in said chamber including a balemember interposed between `said growing and supply region, saidcirculation control means being so constructed and arranged as to deiinein said chamber, and limit communication between said regions to, anupward dow-passage and a downward now-passage, jointly controlling anddirecting the convectional ilow of such a fluid medium due to heatsupplied by said heat supply means, the aggregate minimum llow area ofsaid passages amounting to less than about 20% of the cross-sectionalarea of said chamber, said upward ilow passage being generally annularin cross-section and located in proximity to the Vertical walls of saidabbassa i l chamber, said downward ilow-passagebeing proximate theVverticalV axisofrsaidrchamber` and opening into said supply region asubstantial distance below the location where said upward ilow passageopens intoY said growing region. v c 3. .Apparatus according to claim 2wherein said baille member is shaped to direct upward ilow of such fluidtransfer medium in said supply region radially outwardly toward saidupward ilow-passage and the downward ilow of suchrnediumrin said growingregion radially inwardly toward said downward ilow-passage.

4. Apparatus for the hydrothermal synthesis'of quartz in single crystalform, comprising: means deiining a vertically elongated enclosedcylindrical chamber having a length-to-diameter ratio of from :1 to 15:1and being adapted to contain a fluid transfer medium at temperatures upto about 400 C. and pressures up to 10,000 pounds per square inch, saidchamber having -a quartz growing region occupying at least approximatelyits upper half and a crystalline silica supply region in its lower end;means operative to supply heat to the bottom and to the sides of thegrowing region of said chamber; insulation means surrounding saidchamber, so constructed and arranged to preclude substantial heat lossfrom said supply region and toallow heat loss at a preselected rate fromsaid growing region; a perforate container for crystalline silica supplymaterial disposed and supported inpsaid supply region with substantialclearance between the bottom and sides of said chamber and container,respectively; a transverse baille member in said chamber interposedbetween said supply and growing regions, said baille member being soconstructed and arranged as to dene, and limit communication betweensaid growing and supply regions to, an upward axial `flow-passage and adownward axial ilow-passage, jointly controlling the raterand directingthe path of convectional circulation of such iluid medium, the ilow areaof said passages individually being approximately equal and, in theaggregate, amounting to less than about of the cross-sectional area ofsaid chamber, said upward flow-passage being generally annular incross-section, concentric with the vertical axis of said chamber, andlocated adjacent the sidewalls of said chamber, said downwardilow-passage being of circular crosssection, concentric with saidIvertical axis and opening into said supply region at a locationsubstantially below the upper terminus of said upward flow-passage; andseed holder means in said growing regions adapted to hold a plurality ofquartz seeds in spaced relation and so disposed `as to define asubstantially unobstructed clearance space adjacent the walls of saidchamber and surrounding the seed holder, said clearance space extendingsubstantially the entire length of said growing region from the upperterminus of said upward flow-passage to the top of said chamber.

' 5. Apparatus according to claim 4 wherein said downward ilow-passageincludes a tubular member extending coam'ally downward from said baillemember, through said container, and terminating short of the bottom ofsaid chamber.

' `6. Apparatus for the hydrothermal synthesis of quartz in singlecrystal form, comprisingrvm'eans defining a vertically elongatedenclosed cylindrical chamber having a length to diameter ratio of from5:1 to 15 :1 and being adapted to contain a iluid transfer medium attemperatures up to about 400 C. and pressures up to 10,000 pounds persquare inch, said chamber having a quartz growing region occupying, atleast, approximately the upper half of its length and having acrystalline silica supply region occupying substantially the entireremaining length of said chamber; means operative to supplyV heat to thebottom and sides of the supply region of said chamber; insulation meanssurroundingsaid chamber, sorconstructed and arranged to precludesubstantial heat loss from said supply region and to allow heat loss ata preselected rate from said growing region; an elongated, perforatecon- Vtral opening therethrough; a transverse baille member in saidchamberV interposed between said supply and growing regions, said baillemember containing a central aperture concentric `with the vertical axisof said chamber j and, deiining, with the laterally adjacent side wallsof said chamber, an annular passage between the perimeter of said baillemember and said side walls the area of said aperture and of said passagebeing approximately equal and, in the aggregate, amounting to less thanabout 20% of the cross-sectional area of said chamber; a tubular member,connected to said baille in ilow communication with the said aperture,extending coaxially downward, with substantial peripheral clearance,into the opening in said container and terminating short of the bottomof said chamber; and seed holder means in ysaid growing regions adaptedto hold a plurality of quartz seeds in spaced region and so dispersed asto define an unobstructed clearance space adjacent the walls of saidchamber and surrounding the seed holder, said clearance space extendingsubstantially the entire length of said growing region from the upperside of said baille member to the top of said chamber.

7. Apparatus according to claim 6 wherein said container comprises aplurality of horizontal perforate partitions dividing it into a numberof separate compartments.

8. Apparatus according to claim 6 wherein said baille member is a flatplate.

9. Apparatus according to claim 6 wherein said baille member includes acoaxial hollow cylindrical portion on the perimeter thereof extendingupwardly into said growing region.

l0. Apparatus according to claim 6 wherein the underside of said baillelmember slopes upwardly and outwardly from said aperture to itsperimeter and the upper surface of said baille member slopes inwardlyand downwardly from its perimeter to said aperture.

-l l. Apparatus for the hydrothermal synthesis of quartz in singlecrystal form, comprising: means deiining a vertically elongated enclosedcylindrical chamber having a length to diameter ratio of from 5:1 to 15:l and being adapted to contain a fluid transfer medium at temperaturesup to about 400 C. and pressures up to 10,000 pounds per square inch,said chamber having a quartz growing region at its upper end and asilica supply region at its lower end; :means operative to supply heatto the bottom and sides o f the growing region of said chamber;insulation means surrounding said chamber, so constructed and arrangedto preclude substantial heat loss from said supply region and to allowheat loss at a preselected rate from said growing region; an elongated,perforate container of annular cross-section coaxially disposed andsupported in said growing region with its bottom and outer sides spaced,respectively, from the bottom and side walls of said chamber; atransverse baille member of hollow conical configuration coaxiallydisposed in said chamber between said supply and growing regions withits maximum circumference uppermost and radially inwardly spaced fromthe walls of said chamber so as to dene therewith an annular passage,said baille member having a central aperture in its lower end, the flowarea of said aperture and of said passage being approximately equaland,'in the aggregate, amounting to less than about 20% of thecross-sectional area of said chamber; and seed holder means in saidgrowing regions adapted to hold a plurality of quartzseeds in spacedrelation Vand so disposed as to Vdefine an unobstructed clearance spaceadjacent the walls of said chamber and surrounding the seed holder, saidclearance space extending substantially the entire length of saidgrowingregion from the upper side of said baille member to the topofsaid chamber.

13 14 12. Apparatus according to claim 11 including a tubu- 2,675,303Sobek et al Apr. 13, 1954 lar member connected to said baie in oWcommunica- 2,785,058 Buehler Mar. 12, 1957 tion with said aperture,extending downward with substantial peripheral clearance into saidcontainer and ter- FOREIGN PATENTS minating short of the bottom of saidchamber. 5 682,203 Great Britain Nov. 5, 1952 References Cited in the leof this patent OTHER REFERENCES UNITED STATES PATENTS Walker et a1.:Industrial and Engineering Chemistry,

1,353,571 Dreibrodt Sept. 20, 192V July 1950, v01. 42, No. 7, pages 1369to end.

1. APPARATUS FOR THE HYDROTHERMAL SYNTHESIS OF QUATZ IN SINGLE SRYSTALFORM COMPRISING: MEANS DEFINING A VERTICALLY ENLONGATED ENCLOSED CHAMBERADAPTED TO CONTAIN A FLUID MEDIUM UNDER CONDITIOIN OF HIGH TEMPERATUREAND PRESSURE, AND CHAMBER HAVING A QUARTZ GROWING REGION IN ITS UPPEREND AND A SOURCE MATERIAL SUPPLY REING IN ITS LOWER END; MEANS OPERATIVETO SUPPLY HEAT TO THE LOWER END OF SAID CHAMBER; AND CIRCULATION CONTROLMEANS IN SAID CHAMBER INCLUDING A BAFFLE INTERPOSED BETWEEN SAID GROWINGAND SUPPLY REGIONS, SAID CIRCULATION CONTROL MEANS BEING SO CONSTRUCTEDAND ARRANGED AS TO DEFIN, AND LIMIT FLOW COMMUNICATION BETWEEN SAIDREQIONS TO, AN UPWARD FLOW PASSAGE AND A DOWNWARD FLOW PASSAGE, JOINTLYCONTROLLING AND DIRECTING THE CONVECTIONAL FLOW OF SUCH FLUID TRANSFERMDIUM DUE TO HEAT SUPPLIED BY SAID HEAD SUPPLY MEAN, EACH IF SAIDPASSAGES, INDIVIDUALLY HAVING A CROSS-SECTIONAL AREA RELATIVELY SMALL INCOMPARSION TO THAT OF SAID CHAMBER, SAID DOWNWARD FLOW-PASSAGE BEINGSUBSTANTIALLY CENTRALLY LOCATED WITH RESPECT TO THE VERTICAL CENTERLINEOF SAID CHAMBER, SAID UPWARD FLOW-PASSAGE BEING LOCATED ADJACENT THELATERALLY OUTER LIMITS OF SAID CHAMBER AND OPENING INTO SAID GROWINGREGION A SUBSTANTIAL DISTANCE ABOVE THE LOCATION WHERE SAID DOWNWARDFLOW PASSAGE OPEN INTO SAID SUPPLY REGION.